Electrical musical instrument



Oct. 17, 1939.

- F. A. FIRESTONE ELECTRICAL MUSICAL INSTRUMENT Filed March so, 1936 2Sheets-Sheet 1 INVE T v FLOYD ft. FIRESTONE ATTORNEY A im Q33 Oct. 1.7,1939. F. A. FIRVESTONE 2,176,525

ELECTRICAL MUS I CAL INSTRUMENT Filed March 50, 1936 2 Sheets-Sheet 2 ll i l l l'l ailllmlllllll lkf l l l l l m l T T INVENTOR I BY FLOYD A.FIR-ESTONE A TTORNEY Patented Oct. 17, 1939 UNITED STATES ELECTRICALMUSICAL INSTRUMENT Floyd A. Firestone, Ann Arbor, Mich., assignor toCentral Commercial 00., Chicago, 111., a corporation of IllinoisApplication March 30, 1936, Serial No. .71,ii47

18 Claims.

This invention relates to an electrical musical instrument of the samegeneral class as the one broadly claimed in Letters Patent of the UnitedStates No. 1,953,753 issued to me on April 3, 1934, and has particularreference to certain new and novel features of construction, forms,shapes, arrangements and combination of parts described generally eitherin whole or in part but not shown or claimed in said patent.

A feature of the invention disclosed and broadly claimed in said priorpatent resides in the use of a plurality'of rotary, capacity reactancedevices adapted to produce alternating voltages corresponding with thetones of a musical scale then selectively impressed upon an amplifyingcircuit and the amplified currents converted into audible sound.- Thepatent teaches the use of means by which these capacity reactancedevices can be connected in a control circuit and the growth and decayof the voltages controlled to enable many very desirable tonalpossibilities to be realized.

A further feature claimed broadly in said prior patent relates to anarrangement of rotary capacity reactance devices, each comprising twoplates formed and related to each other to enable the electrostaticcapacity thereof to vary according as a grounded conductor is rotatedbetween them at an assigned speed.

This invention disclosed and claimed in the aforestated prior patentprovides for any one or more of the rotary capacity reactances beingplaced in operation upon depressing the keys of the key manual of anorgan console; the compounding of the difierent tonal components beingeffected by certain multiple switches actuated by said keys. Theinvention provides means for varying as to loudness the. relation of onetone to another, such for instance, a fundamental relative to any oneormore of its harmonics. The growth and decay of a toneis made possible bycertain variable resistances and other-impedances in the circuit betweena polarizing source and said rotary capacity reactances, themathematical theory being that where these impedances are I and claimedin my aforestated prior patent, the invention disclosed and claimedherein has for its essential objects those stated as follows, to wit:

(1) To provide means by which the rate of growth of a tone may be mademore nearly 5 equal to the rate of decay thereof;

(2) To provide means by which the rate of growth of a tone may becontrolled to any desired extent relative to a desired or predeterminedrate of decay thereof;

(3) To provide means by which current of a given frequency can beselectively diverted as and when desired from one portion of a controlcircuit to another according as one musical result or another is desiredas a function of time; b

(4) To provide means by which the growth and decay of a note can whenever desired, be made more instantaneous than was heretofore possible;

(5) To provide means by which, as a function 20 of time, there can beany desired growth anddecay of any note relative to any other note;

(6) To provide means by which any note elicited by actuation of anyparticular key of any manual of the instrument may be controlled 25 toenable (a) a predetermined rate of growth and decay, (b) all or as manynotes as desired to be made as fast or as slow as desired, and (c) noteselicited upon actuation of the keys of one manual to be made fast andthose elicited upon 30 actuating the keys of another manual to be madeslow;

(7 To provide means broadly whereby as many differences in relative timedurations for holding and letting go of the notes may be had as 35desired; l

(8) To provide a rotary capac y reactance device consisting of but tworelatively rotatable members connected between a polarizing source andthe grid of a vacuum tube amplifier;

(9) To provide a rotary capacity reactance device consisting of but tworelatively rotatable members in which one thereof provides a primaryinductor and is formed to produce a multiplicity of frequenciesconforming to different tonal components, and the other thereof servingas a common support for all inductors which are inductivelycomplementary to the frequency determining areas of the primaryinductor. While I suggest a specific order of relationship of thesemembers, wherein a particular one is the primary and the other thesecondary, that this order can be reversed as provided for herein;

(10) To provide simple but exceedingly effective means by which therelative phase of the i tonal components may be shifted. In myexperiments, I discovered that when a strong funda mental and one of itsharmonics are impressed on one ear in various relative phases and soundpressures, the tone quality and the loudness of the combination dependedupon the relative phase of the two components. In a certain phaserelation the loudness of the combination was 3.5 db. less than theloudness of the fundamental alone. Varying the phase changed theloudness of the combination 10 db. and this may be explained by assumingthat the ear mechanism distorts the pure components of a complex soundpressure, producing subjectiveharmonics which may either constructivelyor destructively interfere depending on the relative phases of thecomponents. It is therefore, an important object of my invention toprovide in combination with means for synthetically producing musicallycorrect growth and decay of a tone, a means by which the primary andsecondary inductors of the rotary capacity reactance device will securea phase shift of any harmonic relative to the fundamental, whereby theloudness level and quality of a tone will be musically correct and thetone made more pure and of greater smoothness than was heretoforepossible.

(11) To provide a combination of instrumentalities in which each thereofdepends upon the other for production of musical tones of the greatestpossible purity. To this end, it is generally recognized that with thevarious forms of magnetic pickup devices heretofore employed forproducing frequencies conforming to the different tonal components, itwas impossible to depend upon them for the production of pure tonesbecause it is mechanically impossible to provide rotary wave formproducing members that are dependably uniform. in spite of the greatestpossible care in their making. Where use is made of rotary capacityreactance device, great purity of tone is made possible, and less careneed be used in their manufacture and when the primary and secondaryelements are properly shaped and formed. a dependable pure wave can beproduced. These features plus the fact that respective means areprovided for shifting the phase relation of the tonal components, andfor controlling the growth and decay of a tone insure faithfulreproduction of all tones.

The above and other objects of the invention will be clearly understoodfrom the following detailed description and claims taken in connectionwith the accompanying drawings in which Figure 1 is a schematic view ofa typical portion of an instrument embodying the invention;

Figure 2 is a view in elevation of a set of rotary capacity reactancedevices mounted upon a single shaft and provided with means by which therelative phase of the currents representing the different tonalfrequencies can be varied;

Figure 3 is a view taken substantially in the plane of line 3-3 ofFigure 2;

Figure 4 is a section taken on line 4-4 of Figure 3, and

Figures 5-10, inclusive, are diagrammatic views of different forms ofcircuits and slightly modi fied forms and arrangements of rotarycapacity reactance devices.

In Figure 5 of the accompanying drawings, the control circuit thereinillustrated has its output side connected with the input side of anamplifying circuit, preferable, but not necessarily as shown in Figures1 and 4 of my aforestated prior patent. A rotary capacity reactancedevice capable of producing sufficient alternating voltage to actuatethe grid G of the vacuum tube amplifier I3 is shown at G and isconnected to the polarizing battery 4. This device is substantially thesame as the one disclosed in said prior patent and as shown in Fig. 5,same consists of a metallic disc 2, fixed to a rotatable shaft I andadapted to be driven at an assigned, or predetermined speed by the meansI a. Around the disc is a row of equally spaced holes H or theequivalent thereof. Two metallic plates 3 and 12 constitute stators orinductors at the opposite sides of said disc and are disposed close tothe annular series of holes H so as to be successively alined therewithduring rotational motion of said disc. Incident thereto, and assuming acharging current is being delivered to the primary plate 3, theelectrostatic capacity between plates 3 and I2 and through said holes Hwill vary, the potential of the plate l2 being always greater when saidplate is opposite any one of said holes than when it is opposite animperforate or solid part of said disc, the latter connected in thecontrol circuit and grounded as shown at G Thus, an alternating voltagewill be periodically developed or produced on the inductor 12 which willhave the frequency with which the holes pass said plate. The voltagethus produced is taken into the conventional vacuum tube l3 and may beconverted into audible sound by any suitable well known electrical soundproducer P shown in Figure 1.

The control circuit in which said generator is connected includes theadjustable resistances 5 and 5 in series, the resistance 5 connectingwith the primary plate 3 and the resistance 5 with a switch S. Saidswitch schematically represents a key of the manual of the instrumentand is adjustable from a charging position at fixed contact C to thedischarging position at fixed contact C the latter connected to groundthrough adjustable resistance 1. The circuit includes a source ofpotential 4 for delivery of a charging current to the plate 3 throughaforesaid contact C when switch S is in said full line position shown inFig. 5.

Connected in parallel in the control circuit are fixed condensers 8 and9, such that when the switch S is-in a charging position, the currentflow from battery 4 will be through adjustable resistance'5, tocondenser 8 whose potential rises slowly until energy passes throughadjustable resistance 5", thence to condenser 9, the potential of whichwill also rise slowly. In this manner, a very even rate of attack orrising voltage supply is obtained at plate 3. A correspondingalternating voltage at plate I2 is thereby impressed upon the grid ofsaid amplifier l3. When the switch S is placed in the dotted lineposition shown in Figure 5, the device G is discharged at approximatelythe same rate as it was charged until the voltage value at plate 3 isagain at zero.

In the line of each of the condensers 8 and 9 is a switch 2| which maybe controlled at will from the console of the instrument, so that one orboth said condensers can be selectively placed in open or closedcircuit. By reason of the adjustable resistance 5 and 5 andv theadjustable resistance 1 across the control circuit, it mamfestly followsthat said resistances can be actuated to very accurately govern the rateat which the generator is charged and discharged. When used selectivelyin conjunction with the condenscrs 8 and 3, an exceedingly large numberof changes in the elapsed time between starting and stopping of thecharging of the device G, and be- 76 tween the starting and stopping ofthe discharging of said device can be had. It is possible with properrelative adjustment of the resistances, to

- proportion the rate of attack relative to any desired rate of decay ofa note or contrariwise, and as each device G is adapted to be separatelycontrolled, the period of time for the decay and attack of one note maybe made to be quite different from that of any other note, a feature ofconsiderable importance, when the invention is used in connection with aplural manual instrument. So accurately may this be done, that'therespective elapsed times may be almost, if not exactly equal throughoutthe scale should this be desired by the player, or the device G can bemade to function so that the time interval for the sounding of anyfundamental tone may be in any desired proportion relative to the periodof time for the sounding of any of the harmonics of the fundamental. Ifthe condensers 8 and 9 are placed in open circuit, the only resistanceoffered the flow of current to and from the device G will be through theresistances in the line between the battery and said device.

The control circuit shown in Figure 6 of the drawings is substantiallythe same as the circuit shown in Figure 5, the difference being in theprovision of a rotary capacity reactance device G consisting of primarystator plate 3 and rotary secondary disc 2 the latter connected incircuit with the grid G of amplifier I3 and the former with theadjustable resistance 5 In the form shown in Figure '7, the disc 2 hasits shaft I grounded at 2 and the primary plate 3 is connected withadjustable resistance 5 and with the grid of the amplifier I3 through ablocking condenser I0. The circuit used in this form is in all otherrespect like those first referred to.

In the form shown in Figure 8, the disc 2 is insulated from the groundedshaft I as at I6 and has a slip ring I5 against which the collectorbrush ll of the grid circuit of vacuum tube I3 bears. A primary statorplate 3 is adapted to be connected through adjustable resistance 5 witheither the battery 4 or the adjustable resistance I according as theprimary plate 3 is to be charged or discharged. The circuit is otherwisefunctionally the same as any one of the circuits first referred to.

In Figure 9, the arrangement is substantially the same as that shown inFigure 8, the main difference being in the use of the brush H and disc 2employed as a primary inductor, the plate 3 being thesecondary inductor,whereas, in the form shown in Figure 5, the brush l1 and coacting disc 2mutually provide a secondary inductor. i

In each of the circuits herein disclosed, a grid leak I I is providedacross the circuit as is well known in the art of radio.

The term generator employed herein shall be understood to mean two ormore suitably shaped and relatively rotatable areas insulated from eachother and forming a varying capacity react'ance; whereby an alternatingvoltage conforming to the frequency of a note'in a musical scale can beselectively impressed upon the circult of a vacuum tube system andconverted into audible sound of suitable loudness. Said devicedistinguishes from generators of the magnetic scale and other forms oftone generators of the prior art in that it insures that the outputvoltage s'hallalways be proportional to the capacity of the generator,it being possible to readily control the capacity from minimum tomaximum, whereby the attack on the tones and decay thereof can beregulated to suit the musical taste of the player. The plate circuit I4of the amplifier I3 can be coupled in the control circuit and with theloud speaker through a suitable rheostat R.

In Figure 3, the disc 2 is formed with concentric rows of holes B, therebeing one such row of holes for a fundamental tone and one each for suchof the harmonics as are desired to be used. In practice, the discs of aseries or set in use will generate the fundamental frequenciesdesignated by the following numbers: I, 2, 4, 8, I6, 32, 64, I28 and256. The rest of the rows are used for providing such number ofharmonics of the fundamental tone as are desired. In my prior patent, Iteach the grouping of such discs in sets of three, each driven at 16.00revolutions per second, the arrangement being such that all the Us ofthe scale and all their necessary harmonics can be produced. I also showsuch arrangement of discs in Figure 2. A similar group driven at a speedof 16.95 revolutions per second will produce all the frequenciesrequired for all the C sharps of the scale and their harmonics. Thefrequencies of all the notes of the musical scale and all theirnecessary or desired harmonics can be produced by twelve similargenerator groups running at the following speeds in revolutions persecond; 16.00; 16.95; 17.96; 19.02; 20.15; 21.35; 22.62; 23.97; 25.39;26.90; 28.50; and 30.19, all in the relation of the frequencies of theequally tempered scale, each being larger than the one just preceding bythe twelfthroot of 2.

In Figures 2, 3 and 4 the circumferentially adjustable secondaryinductors I are crescent shaped, being bounded by the two circular arcsA-B and having a total length approximately equal to the distancebetween two circumjacent holes H. The fixed primary inductors I eachconsist of a plate of any shape but essentially considerably larger thanthe secondary plates and disposed adjacent to and directly oppositethereto so that the primary is at one side of the disc and the secondaryat the opposite side thereof. Each secondary plate can be movedcircumferentially either clockwise or counterclockwise relative to itscoacting primary plate, whereby the relative phases of the generatedcurrents can be varied. A pair of inductors shaped and re-- 5% which isthe least amount of harmonic the ear can detect and therefore representsa tone which is for the intended purpose a pure tone.

As shown in Figures 2, 3 and 4,-the entire series of pairs of primaryand secondary inductors for each disc is supported by aradially disposedfixed support I00, comprising parallel spaced arms of hard insulatingmaterial, and on the inner face of one arm' and in longitudinally seriesformation at one side of the disc are the primary conductors 1 Insimilar manner, the secondary conductors I are mounted on the inner faceof the other arm and are thus disposed at the opposite side of the holesH and opposite said primary inductors. The secondary inductors carrystuds II which are passed through arcuateslots I02 in the arm I03, theslots being concentric relative to the axis of.- the disc 2.

Nuts I04 or other equivalent retaining devices relative to said primaryinductors. It obviously follows that by mounting said respective pairsof primary and secondary inductors upon a common fixed support arelative fixed phase shift can be obtained. Should, however, each pairof primary and secondary inductors be mounted separately and forcircumferential movement relative to each other so that they are capableof adjustment representing either a 180% lag or 180% lead, the phasescan be shifted relatively, and such arrangement will provide for theirad- J'ustment as and when desired from the console of the instrument. Ineither such example the relative circumferential shifting of the primaryand secondary inductors will secure a phase shift of any harmonicrelative to the fundamental and the loudness and quality of the tonethereby beneficially influenced musically and a tone of great purity andsmoothness thereby produced.

Although the invention has been illustrated and described in connectionwith certain specific circuit arrangements it is to be understood thatit is not to be limited either to the particular arrangment as a whole,or to particular details, but only by the scope of the appended claims,which latter, I shall expect to be broadly construed to cover a largerange of modifications because of the correspondingly large number ofhook-ups herein disclosed, any one of which is the electrical equivalentof the other. I have illustrated a variety of circuits merely to showthe many known ways of controlling the time intervals between chargingand discharging of any generator of the series employed.

In Figure 1 six rotary capacity reactances are illustrated. The keycircuit is the same as the one disclosed in my prior patent and it willsuffice to say that each key such as the one shown at will include asmany circuit making and breaking contact devices as are required tosimultaneously close as many reactance assemblies as there arecomponents of a tone to be compounded and to open the circuit to enablethe assemblies to be discharged as elsewhere set forth herein. Theassemblies shown in this view are six in number and while each assemblymay include a separate rotary disc, all the frequencies for thefundamental and its harmonics can be formed on a single disc as shown inFigure 2.

In Figure 10 a portion of the output side of a control circuit is shown,and I suggest that in the line to the primary inductor I06 of the rotarycapacity reactance device I01, there be interposed an iron coreinductive reactance I08. This is preferably used to take the place ofthe adjustable resistance nearest the secondary inductor. Suchresistance would specifically be the one indicated at 5 in any one ofthe control circuits first described. However, this reactance may beused in association with any series multiple arrangement of resistances5 and 5 and pressure retarding or blocking condensers 8 and 9. In thefigure, a condenser 9 is connected in shunt and disposed betweeninductor I06 and said reactance. The condenser 8 is connected withadjustable resistance 5 in series with said reactance 108.

It is to be borne in mind that all switches in the control circuit willbe controlled from the key manual or manuals of the instrument and mayeither be preset or can be controlled by the player as and when desiredwhile the organ is being played, The switches associated with the keysof one manual may be preset to for slow growth and decay and thoseassociated with another manual set for a fast growth and decay. Byreason thereof, and bearing in mind that the switches can be separatelyactuated, it follows that a great variety of effects can be had.

It therefore follows that the rate of attack and delay for any onequality on one manual can be regulated and pre-set so that the properattack and delay for a quality will be introduced when a tappet ispressed that brings that quality into play. Certain qualities such asdiapasons and soft flutes will have a slow rate of attack and otherssuch as the clarinet and oboe will have a faster rate of attack whilestill others such as marimba or vibraharp will have a rapid attack.

The rate of attack and delay may be different for a quality on onemanual than it is for another quality on another manual. That is to say,a clarinet with a fast attack may be used on one manual while a flutewith a slow attack may be used simultaneously on the other manual.

while certain remaining components will have a slow attack and will havea longer delay. This will be found to be particularly useful in chimesin which certain of the sub tones will have a long delay while thehigher harmonics will drop out rapidly after a sudden percussive attackwhen the key is depressed. Certain other qualities such as diapason maybe subject to such treatment in moderation.

Thus it is possible to have a quality on one manual in which thecomponents vary relative to each other, while on another manual anotherquality may be used which has a uniform attack and delay on all partialsof that quality in which the components may vary in the rate of attackas omthe first manual.

Regarding the form of rotary capacity reactance device shown in Figure'7, I wish particularly to direct attention to the fact that directcurrent is conducted to the inductor 3a from the direct current source 4and that the grid G of the tube I3 is directly connected with saidinductor 3a by a metallic conductor. Bearing in mind that the metal disc2 is inductively related to the inductor 3a and is driven at a constantpredetermined speed, and that it is formed as in all other examples ofthe invention with an annular series of openings H, it is evident thatsaid disc functions as a converter and that the direct current deliveredto the inductor is changed into pulsating direct current, the frequencyof which will determine the tone generated at the sound producer P.

Regarding the series multiple circuits employed in each form of theinvention, it is important to note that in addition to its being madepossible to cut into and out of the circuit any one or more of thecapacity condensers 8 and 9, it is possible to selectively control therate at which these condensers can be charged and discharged by merelyadjustably connecting said condensers with said resistances 5 and 5a.The resistances thus serve the dual capacity of a means for placing inthe line between source I and rotary reactance device G any amount ofresistance desired and to cause the condensers to be charged anddischarged as quickly or as slowly as desired. This is, of course,assuming that the switches 2| are in closed circuit positions.

It is to be understood that the condensers 8 and 9 may be of differentcapacities to thereby increase the range of usefulness of the instrumentfor the purposes set forth herein.

'What is claimed is:

1. In an electrical musical instrument, a .ca-

pacity reactance device comprising stator and rotor elements adapted tobe driven at a constant relative speed and having respective surfacesfor producing voltages conforming to the vibrational frequencies of afundamental tone and its harmonies; and means by which the elements canbe shifted relatively circumferentially to vary the relative phases ofthe produced voltages.

2. In an electrical musical instrument, rotary capacity reactancedevices for producing alternating current voltages conforming to thevibrational frequencies of the fundamental tones of a musical scale andthe harmonics thereof; a polarizing source for said devices; a circuitcommon to said devices; a circuit having a vacuum tube amplifier, thegrid of which is connected with said common circuit and adapted tobeactuated by current impressed thereon; an electrical sound producerconnected in circuit with said amplifier; means by which a phase shiftcan be made between a fundamental frequency producing device and any oneor more devices for producing frequencies conforming to the harmonics ofsaid fundamental frequency; means in said'common circuit between theaforementioned polarizing source and said frequency producing devicesfor controlling the rate at which any one of said devices can be chargedand discharged; and means by which said controlling means can be placedin either open or closed circuit with said polarizing source.

3. In an electrical musical instrument, an electrical sound producer; anelectrical circuit for controlling the operation of said sound producer;and a capacity reactance device comprising a pair of stator elements andan intermediate rotor element formed to control the effective capacityreactance of said circuit at predetermined tone frequencies; one of saidstators having inductors facing one side of the rotor; the other statorhaving inductors facing the other side of the rotor and disposedopposite the first inductors and being capable of circumferentialadjustment relative to said first inductors so that the relative phaseof the frequencies produced by said reactance can be varied.

' 4. In an electrical musical instrument, an electrical sound producer;an electrical circuit for controlling the operation of said soundproducer;

and a capacity reactance device comprising a pair of stator elements andan intermediate rotor element formed to control the effective capacityreactance of said circuit at predetermined tone frequencies; one of saidstators having inductors facing one side of the rotor; the other statorhaving inductors facing the other side of the rotor and disposedopposite-the first inductors and being capable of circumferentialadjustment relative to said first inductors so that the relative phaseof the frequencies produced by said reactance can be varied, the firstand second named inductors being shaped so that the harmonic content ofany generated frequency is inaudible.

5. In an electrical musical instrument, means for eiectrostaticallyproducing an alternatingcurrent of the frequency of a predeterminedsound wave, said means comprising oppositely disposed stators, adaptedrespectively to be connected in 'circuit with a sound producer and witha polarizing source; and a rotary shield disposed between said statorsandspaced apart therefrom and having portions for alternately exposingsaid stators to each other; and means enabling the positions of saidstators to be shifted relative to each other and to said stator exposingportions of said rotary shield to thereby control the phase of theproduced current.

6. In an electrical musical instrument, an electrostatic tone generatorembodying a current conductor adapted to be electrically connected tothe grid of an electron tube; a rotatable shaft having fixed thereto andinsulated therefrom a metallic disc, disposed substantially parallel toand spaced apart from said conductor and having a portion in concentricrelation to the axis of rotation of the shaft formed so that as theshaft is rotated at an assigned, constant speed, the electrostaticcapacity between said member and the conductor will vary periodicallywith resulting production of alternating voltage by the generator, thefrequency of which conforms to a predetermined musical tone.

7. In an electrical musical instrument employing a space discharge tubehaving input and output circuits and a loud speaker coupled to theoutput circuit so as to be actuable to convert variable currents intoaudible sound of controlled volume; generators for producing variablecurrents at different tone frequencies; an electrical network includinga polarizing source for said generators; adjustable series impedancesthrough which voltage is supplied a generator; condensers in parallelwith the respective impedances of a generator; and means actuable from aconsole for selectively rendering active relative to a generator, one ormore of the condensers and for adjusting the impedances to govern therate at which the generator builds up its voltage through said supplyimpedances.

8. In an electrical musical instrument employing a space discharge tubehaving input and output circuits and a loud speaker coupled to theoutput circuit so as to be actuable to convert variable currentsintp'audible sound of controlled volume; generators for producingvariable currents at different tone frequencies; an electrical networkincluding a polarizing source for said generators; means by which therelative phases of the currents can be varied; adjustable seriesimpedances through which voltage is supplied a generator; condensers inparallel with the respective impedances of a generator; and meansactuable from a console for selectively rendering aetive relative to agenerator, one or more condensers and for adjusting the impedances togovern the rate at which the generator builds up its voltage throughsaid impedances.

\ 9. In an electrical musical instrument employing a space dischargetube having input and output circuits and a loud speaker coupled to theoutput circuit so as to be actuable to convert variable currents intoaudible sound of controlled volume; generators for producing variablecurrents at different tone frequencies; an electrical network includinga polarizing source forsaid generators; means for predetermining theelectrical value of voltage supplied a generator from said source;adjustable series impedances through which voltage is supplied saidgenerators; condensers in parallel with the respective impedances of agenerator; and means actuable from a console for selectively renderingactive relative to a generator, one or more condensers and for adjustingthe impedances to govern the rate at which the generator builds up itsvoltage through said impedances.

10. In an electrical musical instrument employing a space discharge tubehaving input and output circuits, an electrical sound producer actuableby current in the output circuit and an electrical network including apolarizing source; alternating current generators adapted to bepolarized from said source; series impedances in said network betweeneach generator and the source; condensers in parallel in said network;means by which the condensers can be selectively connected with acorresponding number of impedances and charged therethrough; and keycontrolled means for connecting the impedances with said source upondepression of said key and in series with a resisted discharge path whenthe key is raised.

11. In an electrical musical instrument employing a space discharge tubehaving input and output circuits and a loud speaker actuable by currentin the output circuit; means for producing a variable current ofpredetermined waveform in said output circuit, said means comprising incombination with a polarizing source, a continuously variablecapacitance device including an electrode having a planar capacity areaof substantially crescent configuration and a rotational scannerdisposed in spaced parallel relation to said capacity area to provide athin air dielectric between same and the scanner and servingperiodically to coact with the scanner electrostatically to produce inthe input circuit variable current of said predetermined waveform.

12. An electrical musical instrument comprising a work circuit havingmeans for converting alternating voltage into audible sound; a condenserhaving capacity areas of substantially crescent shape, and means formed,disposed and adapted simultaneously to scan said areas to thereby causecontinuous cyclic capacitance changes and production of alternatingvoltages at said areas of respectively different tone frequencies, eachsubstantially of sinusoidal wave form; and keying means enablingselective conduction of alternating voltages to said work circuit fromany one or more of said electrodes.

13. An electrical musical instrument comprising a work circuit havingmeans for converting amplified alternating voltage into audible sound; acondenser having capacity areas, each substantially of crescent shape,and means formed, disposed and adapted simultaneously to scan said areasto thereby cause continuous cyclic capacitance changes at the areas andproduction of alternating voltages of respectively different tonefrequencies, each substantially of sinusoidal waveform; and means bywhich preselected voltages can be conducted to said work circuit atpredetel-mined relative intensities.

14. A device for. producing alternating voltage of predetermined tonefrequency and substantially sinusoidal waveform comprising a capacitancereactance; means for polarizing said reactance, said reactance includingsubstantially crescent shaped pattern areas of electrical conductivematerial; and continuously driven means for sequentially scanning saidareas.

15. A device for producing alternating voltage of predetermined tonefrequency and substantially sinusoidal waveform comprising a capacitancereactance; means for polarizing said reactance, said reactance includinga metallic pattern substantially of crescent shape and continuouslydriven means having scanning portions spaced apart from each other andsequentially scanning said pattern to periodically vary the capacitanceof the reactance according to a substantially sinusoidal waveform andproduce a corresponding alternating voltage; an electrical networkhaving an electron tube amplifier provided with input and outputcircuits; an electrical sound producer connected in the output circuitand responsive to actuation of the amplifier; keying means for causingconduction of the voltage to the input circuit; and means in the networkfor controlling the growth and decay of a tone at said sound producer.

16. In an electrical musical instrument, alternators having relativelymovable planar parts, respectively of precalculated shapes and forms,said parts coacting to produce alternating voltages of different tonefrequencies; means for synthesizing such of the. produced voltages asare desired for the production of a desired complex waveform; means forcontrolling the relative intensities of said voltages; and means forshifting the phase relation of said voltages.

17. In an electrical musical instrument employing a space discharge tubehaving input and output circuits, an electrical sound producer actuableby current in the output circuit, an electrical network, means fordelivering electrical impulses at different tone frequencies to saidinput circuit through said network, said network including series andparallel connected paths, impedance means in said series connected path,condensers in said parallel connected paths, key controlled means forselectively controlling the aforesaid delivery of impulses to said inputcircuit, and means for rendering said condensers selectively effectivefor controlling the curve characteristics of impulses in the outputcircuit of said space discharge tube.

18. In, an electrical musical instrument employing a space dischargetube having input and output circuits, an electrical sound produceractuable by current in the output circuit, an electrical network, meansfor delivering electrical impulses corresponding to musical tones to theinput of said space discharge tube through said network, said networkincluding series and parallel connected paths, impedance elements insaid series connected path, condensers in said parallel connected pathsand key controlled means for selectively controlling the impression ofelectrical impulses upon said input circuit from said network and meansin selected parallel connected paths for rendering the condenserstherein effective for selectively controlling the operatingcharacteristics of said network.

FLOYD A. FIRE-STONE.

